Call Catalina
Had a leaky tank in my 84 Cat 30. Purged it and had it welded (aluminum tank). Still leaked. Did it again. Still had leak (bottom was full of tiny holes). Called Catalina, about $250 and had a perfectly fitting tank. The gauge of aluminum has been increased too. Now I make sure to clean out crud on bottom by suction (water, algae) and use a stabilizer. The great thing about Catalina is that they are there and can provide replacement parts for their boats. Just call Catalina.
